Shrink Pots

How it works

A shrink pot (shrink box) is a hollowed section of a green branch with a dry bottom set into a groove near its base. As the green wall dries, it shrinks around the circumference and clamps the bottom tight, no glue or nails ¹. It’s wood movement - usually the enemy - put to work. Sundqvist’s sloyd decorates them with carving and paint ².

Choosing the round

• Birch is the favorite; maple, alder, and aspen work too. Avoid aromatic woods like cedar for food ¹.
• Fresh and knot-free, with the pith near the center.
• 5 inches (13 cm) in diameter or smaller is easier for a first pot ¹.
• Cut it a bit longer than the finished pot and keep it wet until you work it.

Hollowing

1. Core the center with a T-auger, brace and bit, or a drill press and Forstner bits, removing the pith (which would crack) ¹.
2. Hollow to the layout line with a long-handled hook knife or gouges, leaving a little to smooth ¹.
3. Remove the bark and shape the outside with a drawknife or knife, staying just outside the outer line.
4. Aim for even walls about 3/8 in. (10 mm) all the way around ¹. Thick walls hold more water and shrink more; uneven walls crack.

Work in one session if you can, or keep the pot wrapped so it doesn’t start drying early.

The groove

Cut a groove inside the wall about 1/2 in. (12 mm) above the bottom edge, roughly 1/8 in. (3 mm) deep, with a V-shaped profile. A knife works; Byrd uses a scorp for the channel ¹. Keep it level all the way around so the bottom sits flat.

The bottom

• Dry wood, ideally a thin board of the same or similar species, about 3/8 in. thick. A wet bottom would shrink along with the wall and loosen.
• Trace the inside of the pot at the groove and cut the bottom slightly oversize, so it must be sprung into the groove.
• Bevel its edge to match the V of the groove.
• Squeeze the green pot slightly oval and pop the bottom in. As the wall dries over the next days, it locks the bottom in.

Lid and finish

The lid is a dry disc that fits inside the rim, with a knob or a carved handle. Fit it after the pot has dried fully - fit it green and it’ll jam as the wall shrinks. Decorate the outside with chip carving, kolrosing, or paint while it’s still slightly damp or after it dries; oil inside and out with a drying oil.

What to take from this

A shrink pot uses wet-dry joinery: a hollowed green birch round with even 3/8-in. walls clamps a dry, beveled, slightly oversize bottom in a V-groove as it dries. Core out the pith, hollow with a hook knife, cut the groove level, spring the bottom in while the wall is wet, and fit the lid only once the pot is dry.